The feasibility of a spacecraft power system using lithium-ion capacitors (LICs) as the energy storage source is analyzed and compared with a system that uses lithium-ion batteries (LIBs). The mass of the LIB- and LIC-based power systems, including photovoltaic (PV) arrays, are compared at various depth of discharge (DoD) levels. The LIC-based system at a deep DoD of 60-80% can be comparable with the LIB-based system at a DoD more shallow than 20% with respect to the system mass.